1. Field of the Invention
The present invention generally relates to computer apparatus and, in a preferred embodiment thereof, more particularly relates to configurational aspects of the interconnected motherboard/riser card portion of a computer.
2. Description of Related Art
As conventionally constructed, a desktop personal computer has an external housing or chassis within which a main system circuit board (commonly referred to as the "motherboard") is operatively disposed. The motherboard is typically mounted adjacent and parallel to the bottom wall of the housing and has the computer's central processing unit (CPU) and other electronic components of the computer operatively positioned on the top side thereof. Transversely secured to the motherboard, and projecting upwardly therefrom, is a riser card--another printed circuit board having expansion slots thereon to which various expansion cards may be operatively coupled.
In order to facilitate the construction of computers by permitting their manufacturers to purchase interchangeable motherboard and riser card subassemblies from a variety of suppliers, two industry-standard form factors--the "LPX" standard and the "NLX" standard--have been at least unofficially adopted as to the configurational aspects of the necessary motherboard/riser card subassembly portion of the desktop computer. Despite the fabricational and multi-source purchasing benefits obtained by using these industry-standard form factors, each has proven to present certain well-known serviceability limitations.
When the LPX motherboard/riser card form factor is utilized, the riser board contains the PCI and ISA expansion slots, and a bottom connection edge portion of the riser card removably plugs into an elongated connector socket generally centrally disposed on the top side of the motherboard. The motherboard is disposed within the computer housing chassis and removably screwed to the bottom wall of the chassis. The necessary I/O cables (for the serial port, parallel port, keyboard, mouse, etc.) extend inwardly through the back side of the computer housing and are removably plugged into suitable connectors mounted on a rear edge portion of the motherboard. Cables from various internal components of the computer (for example, the power supply unit, IDE, floppy drive, speaker, etc.) are removably secured to suitable connectors on the top side of the motherboard.
In order to remove the motherboard for service or upgrade purposes it is necessary, when the LPX form factor is employed, to perform a rather tedious five step process--namely, (1) unplug the I/O cables from the rear edge of the motherboard (which often also include cables connected to various add-in cards); (2) vertically unseat the riser card from the motherboard; (3) unplug the internal component cables from the motherboard; (4) unscrew the motherboard from the chassis; and (5) lift the unscrewed motherboard upwardly out of the chassis. Of course, subsequently reinstalling the motherboard and riser card subassembly within the chassis requires counterparts to each of these five steps.
One previous attempt to modify and provide enhanced serviceability to the LPX form factor is illustrated and described in copending U.S. patent application Ser. No. 08/681,060 filed on Jul. 22, 1996, entitled "MODULAR DESKTOP COMPUTER HAVING ENHANCED SERVICEABILITY," and assigned to the same assignee as the present application. In such copending patent application, an LPX form factor motherboard and riser card assembly was illustrated as being modified by securing the motherboard to a tray structure which could be slid out the rear I/O connection side of the computer chassis, and by securing the riser card to an upwardly movable "cage" structure which facilitated the upward unplugging of the riser card from the motherboard. This modification to the LPX form factor eliminated the necessity of unplugging the I/O cables from the motherboard in order to remove it from the chassis, and eliminated the necessity of unscrewing the motherboard from the chassis before removing the motherboard.
From an overall serviceability standpoint, the NLX motherboard/riser card form factor represents an appreciable improvement over the unmodified LPX form factor. Specifically, when the NLX form factor standard is utilized, the internal component cables plug into the riser card instead of into the motherboard, and an elongated connector socket on a lower side edge portion of the riser card removably receives, in a horizontal direction, a corresponding connector side edge portion of the motherboard, the length of such connector side edge portion extending transversely to the rear motherboard edge upon which the I/O connectors are disposed. To remove the motherboard when the NLX form factor is used only three steps are required--namely, (1) unplug the I/O cables connected to the motherboard from the rear of the unit; (2) horizontally unseat the motherboard from the riser card; and (3) horizontally slide the unseated motherboard out the side of the chassis. Counterparts to these three steps must be later performed to reinstall the motherboard within the computer chassis.
Various well-known disadvantages and limitations are associated with each of these previously utilized motherboard/riser card form factors. For example, the LPX form factor (even as modified as shown in copending U.S. application Ser. No. 08/681,060) requires that the internal cables be unplugged from the motherboard before it can be removed from the chassis. The NLX form factor requires that the external I/O cables be unplugged from the motherboard before it can be removed from the chassis.
Furthermore, neither the LPX form factor (either in its standard configuration or its modified configuration discussed above) nor the NLX motherboard/riser card form factor is particularly well suited for use in a computer which incorporates more than one "device bay" therein. A device bay is basically an internal bay area within the computer chassis into which a modular computer device (such as a CD ROM drive, a hard drive or a floppy drive) may be operatively and removably inserted from the exterior of the computer. The insertable modular device typically has a connector on its back end which mates with a corresponding bay connector structure in response to insertion of the device into the bay, the bay structure connector structure, in turn, being cabled to the motherboard or the riser card depending upon which motherboard/riser card form factor is being utilized.
Each device bay requires a 1394 (an industry standard high speed serial bus) port and a USB (an industry standard medium speed serial bus) port--no daisy chaining or sharing of ports is allowed. Thus, a computer with two device bays requires two dedicated 1394 ports and two dedicated USB ports. Furthermore, each bay is connected to a Device Bay Controller (DBC) which communicates to the system, typically over a serial bus such as I.sup.2 C (or SMBus) or USB.
In the most cost effective implementation of a multiple device bay system there is a single 1394 PHY device (a bus driver for the host controller), and a USB root hub that feed the bays. The LPX form factor is not a good choice for multiple device bays due to the additional cabling that would be required between the device bays and the motherboard. The NLX form factor, in which a single 1394 PHY and host controller are incorporated on the motherboard, has some built-in device bay interconnection capability. However, the NLX motherboard edge connector (the interface between the motherboard and riser card) only has support for a single 1394 port. Therefore, a two device bay system requires a secondary 1394 PHY to expand that single port to two (or more) ports. In that scenario, according to the Device Bay specification, a USB DBC must be used. Because of this requirement, the multi-device bay design incurs a substantial cost penalty due to the second PHY and a more complex (and therefore expensive) DBC.
As can be seen from the foregoing, both of the current LPX and NLX motherboard/riser card form factors have associated therewith a variety of problems and limitations relating both to serviceability and device bay support. It is to these problems and limitations that the present invention is directed.